1. Field of the Invention
The present invention relates generally to the art of making Al(PO.sub.3).sub.3 and more particularly to the preparation of the B-form of aluminum trimetaphosphate.
2. The Prior Art
Crystalline condensed aluminum phosphates are described in the literature by D'Yvoire, who identified a cyclic aluminum tetrametaphosphate, the stable A-form of Al(PO.sub.3).sub.3, and four long-chain polyphosphates, the B, C, D and E forms of Al(PO.sub.3).sub.3. According to D'Yvoire, these crystalline condensed aluminum metaphosphates are produced by reacting P.sub.2 O.sub.5 and Al.sub.2 O.sub.3 in a molar ratio of 4 to 15 over several hours.
U.S. Pat. No. 4,216,190 to Neely teaches a method for preparing predominantly the B-form of aluminum trimetaphosphate by the addition of an ammonia compound to a solution of aluminum dihydrogen phosphate, Al(H.sub.2 PO.sub.4).sub.3. A white precipitate is formed, which is directly converted to the B-form of aluminum trimetaphosphate, Al(PO.sub.3).sub.3, by a single elevated temperature treatment.
In a study of the effects of grinding on the structure and properties of various aluminum phosphates. Tsuhako et al. report mixing .alpha.-alumina and ammonium dihydrogen phosphate, and heating at 500.degree. to 550.degree. C. for 20 hours to obtain the B-form of Al.sub.4 (P.sub.4 O.sub.12).sub.3.